Autocrine interleukin-6 production and highly malignant multiple myeloma: relation with resistance to drug-induced apoptosis

In this study, flow cytometry was used to evaluate interleukin-6 (IL-6) production by bone marrow mononuclear cells from 47 patients with multiple myeloma (MM) in different clinical stages and 15 patients with monoclonal gammopathy of undetermined significance. In patients with MM, autocrine IL-6 production paralleled the clinical disease stage. The largest proportion of syndecan-1(+)/IL-6(+) cells was detected in patients with resistant relapse or primary refractory disease, suggesting that tumor progression involves expansion of myeloma cells producing IL-6. The authors assessed autocrine IL-6 production and in vitro proliferation and apoptosis of myeloma cells in 6 myeloma cell clones (MCCs) and in 2 myeloma cell lines, namely IM-9 and U-266-1970, which showed different sensitivities to the addition of exogenous IL-6. Autocrine IL-6 production was observed in IL-6-independent MCC-2, MCC-3, and MCC-5 cloned from patients with aggressive disease and in the IM-9 cell line. In contrast, IL-6-dependent MCC-1, MCC-4, and MCC-6 were syndecan-1(+) and IL-6(-). Blocking experiments with anti-IL-6 monoclonal antibody from clone AH65, which binds IL-6-IL-6Ralpha complexes, prevented cell proliferation of IL-6(+) MCCs. Flow cytometry evaluations after propidium iodide staining revealed different susceptibilities of MCCs to cell death. IL-6-producing MCCs showed minimal spontaneous and dexamethasone-induced apoptosis, whereas a regular amplitude of apoptosis occurred in the IL-6(-) MCCs. These data provide evidence that autocrine IL-6 reflects a highly malignant phenotype of myeloma cells. In fact, autocrine IL-6 production and deregulated apoptosis may induce expansion of selective IL-6(+) myeloma cells resistant to spontaneous and drug-induced cell death.     

Plasma cells induce apoptosis of pre-B cells by interacting with bone marrow stromal cells

By using two-color phenotypic analysis with fluorescein isothiocyanate- anti-CD38 and phycoerythrin-anti-CD19 antibodies, we found that pre-B cells (CD38+CD19+) signifcantly decreased depending on the number of plasma cells (CD38++CD19+) in the bone marrow (BM) in the cases with BM plasmacytosis, such as myelomas and even polyclonal gammopathy. To clarify how plasma cells suppress survival of pre-B cells, we examined the effect of plasma cells on the survival of pre-B cells with or without BM-derived stromal cells in vitro. Pre-B cells alone rapidly entered apoptosis, but interleukin-7 (IL-7), a BM stromal cell line (KM- 102), or culture supernatants of KM-102 cells could support pre-B cell survival. On the other hand, inhibitory factors such as transforming growth factor-beta1 (TGF-beta1) and macrophage inflammatory protein- 1beta (MIP-1beta) could suppress survival of pre-B cells even in the presence of IL-7. Plasma cells alone could not suppress survival of pre- B cells in the presence of IL-7, but coculture of plasma cells with KM- 102 cells or primary BM stromal cells induced apoptosis of pre-B cells. Supernatants of coculture with KM-102 and myeloma cell lines (KMS-5) also could suppress survival of pre-B cells. Furthermore, we examined the expression of IL-7, TGF-beta1, and MIP-1beta mRNA in KM-102 cells and primary stromal cells cocultured with myeloma cell lines (KMS-5). In these cells, IL-7 mRNA was downregulated, but the expression of TGF- beta1 and MIP-1beta mRNA was augmented. Therefore, these results suggest that BM-derived stromal cells attached to plasma (myeloma) cells were modulated to secrete lesser levels of supporting factor (IL- 7) and higher levels of inhibitory factors (TGF-beta1 and MIP-1beta) for pre-B cell survival, which could explain why the increased number of plasma (myeloma) cells induced suppression of pre-B cells in the BM. This phenomenon may represent a feedback loop between pre-B cells and plasma cells via BM stromal cells in the BM.     

Vascular endothelial growth factor and interleukin-6 in paracrine tumor-stromal cell interactions in multiple myeloma

Vascular endothelial growth factor (VEGF), a multifunctional cytokine, potently stimulates angiogenesis including tumor neovascularization. Although well established in solid tumors, the role of VEGF in bone marrow neoangiogenesis and paracrine tumor-stromal cell interactions in lymphohematopoietic malignancies has not been fully elucidated. In multiple myeloma (MM), marrow neovascularization parallels disease progression. This parallel prompted us to investigate the expression and secretion of VEGF by myeloma cells and its potential effects in myeloma-marrow stroma interactions. The biologically active splice variants VEGF165 and VEGF121 were expressed and secreted by myeloma cell lines and plasma cells isolated from the marrow of patients with MM. As shown by immunocytochemistry or RT-PCR, myeloma cells did not express or weakly expressed the VEGF receptors FLT-1 and FLK-1/KDR, indicating that autocrine stimulation is unlikely. In contrast, FLK-1/KDR was abundantly expressed by marrow stromal cells. Therefore, we studied the effects of VEGF on marrow stroma, focusing on the secretion of interleukin-6 (IL-6), a potent growth factor for myeloma cells and an inhibitor of plasma cell apoptosis. Exposure of stromal and microvascular endothelial cells to recombinant human (rh) VEGF165 or VEGF121 induced a time- and dose-dependent increase in IL-6 secretion (14- to 27-fold at 50 ng/mL after 24 hours, P <.001). Conversely, rhIL-6 stimulated VEGF expression and secretion in myeloma cell lines (40%-60%; P <.05) and to a variable degree (up to 5.3-fold; P <.005) in plasma cells purified from the marrow of patients with MM. This mutual stimulation suggests paracrine interactions between myeloma and marrow stromal cells triggered by VEGF and IL-6. (Blood. 2000;95:2630-2636)     

Primary tumor cells of myeloma patients induce interleukin-6 secretion in long-term bone marrow cultures

Long-term bone marrow cultures (LTBMC) from patients with multiple myeloma (MM) and normal donors were analyzed for immunophenotype and cytokine production. Both LTBMC adherent cells from myeloma and normal donor origin expressed CD10, CD13, the adhesion molecules CD44, CD54, vascular cell adhesion molecule 1, very late antigen 2 (VLA-2), and VLA- 5, and were positive for extracellular matrix components fibronectin, laminin, and collagen types 3 and 4. LTBMC from myeloma patients and normal donors spontaneously secreted interleukin-6 (IL-6). However, levels of IL-6 correlated with the stage of disease; highest levels of IL-6 were found in LTBMC from patients with active myeloma. To identify the origin of IL-6 production, LTBMC from MM patients and normal donors were cocultured with BM-derived myeloma cells and cells from myeloma cell lines. IL-6 was induced by plasma cell lines that adhered to LTBMC such as ARH-77 and RPMI-8226, but not by nonadhering cell lines U266 and FRAVEL. Myeloma cells strongly stimulated IL-6 secretion in cocultures with LTBMC adherent cells from normal donors and myeloma patients. When direct cellular contact between LTBMC and plasma cells was prevented by tissue-culture inserts, no IL-6 production was induced. This implies that intimate cell-cell contact is a prerequisite for IL-6 induction. Binding of purified myeloma cells to LTBMC adherent cells was partly inhibited by monoclonal antibodies against adhesion molecules VLA-4, CD44, and lymphocyte function-associated antigen 1 (LFA-1) present on the plasma cell. Antibodies against VLA-4, CD29, and LFA-1 also inhibited the induced IL-6 secretion in plasma cell-LTBMC cocultures. In situ hybridization studies performed before and after coculture with plasma cells indicated that LTBMC adherent cells produce the IL-6. These results suggest that the high levels of IL-6 found in LTBMC of MM patients with active disease are a reflection of their previous contact with tumor cells in vivo. These results provide a new perspective on tumor growth in MM and emphasize the importance of plasma cell-LTBMC interaction in the pathophysiology of MM.     

CD40 ligand triggered interleukin-6 secretion in multiple myeloma

Previous studies have suggested that interleukin-6 (IL-6) may mediate growth of multiple myeloma (MM) in either an autocrine or paracrine growth mechanism. However, those molecules which can trigger IL-6 secretion either by tumor cells or non-MM marrow cells are not well characterized. In the present study, we have examined the expression and functional significance of CD40 on MM and plasma cell leukemia (PCL) cells and derived cell lines, as well as long-term bone marrow stromal cells (BMSCs) and derived cell lines. CD40 was expressed on the majority of MM cells (> 90%) and BMSCs (> 70%). Triggering via CD40 using NIH3T3 CD40 ligand transfectant (CD40LT) cells increased (> 30%) cell surface CD80, CD18, CD11a, CD11b, and CD11c expression on MM cell lines. Culture with either fresh or paraformaldehyde fixed NIH3T3 CD40LT cells upregulates IL-6 secretion in MM cells and MM-derived cell lines, as well as normal and MM bone marrow mononuclear cells (BMMCs), BMSCs, and BMSC lines; this effect can be specifically blocked by anti- CD40 monoclonal antibody (MoAb). BMMCs and BMSCs from patients with MM secreted significantly more IL-6 than those from healthy donors (n = 3, P < .001); moreover, after stimulation using CD40L, IL-6 secretion was fourfold greater (n = 3, P < .001) from MM BMMCs and BMSCs than from normal BMMCs and BMSCs. Myeloma (CD38+CD45RA-) cells and non-MM (CD38+CD45RA+, CD38-CD45RA+, and CD38-CD45RA-) BMMCs were separated by dual fluorescence cell sorting. The latter secreted fourfold more IL-6 than the former (n = 2, P < .001). Increased IL-6 secretion (up to 28- fold) and proliferation (Stimulation index 10) by CD38+CD45RA-MM cells was triggered by culture with NIH3T3 CD40LT cells. Finally, anti- CD40MoAb partially (30%) blocked tumor cell to BMSC adhesion-induced IL- 6 secretion. These studies support the view that CD40L may trigger IL-6 secretion by both MM cells and BMSCs and that IL-6-mediated autocrine and paracrine growth mechanisms may be possible in MM.     

Expression of IL-6 and IL-6 receptors by circulating clonotypic B cells in multiple myeloma: potential for autocrine and paracrine networks

OBJECTIVE: To investigate the participation of clonotypic MM B cells in the IL-6 network in patients with multiple myeloma. METHODS: CD19(+) B cells from 45 patients with multiple myeloma and from 18 healthy donors were sorted and their expression of IL-6, IL-6 receptor (CD126) characterized by flow cytometry, in situ RT-PCR, and ELISA measurement of IL-6 and soluble IL-6R. Expression of CD31 was detected by flow cytometry. RESULTS: Interleukin-6 (IL-6) is a pleiotropic cytokine often overexpressed in multiple myeloma (MM). IL-6 induces growth and inhibits apoptosis of MM plasma cells, and upregulates the activity of osteoclasts. MM plasma cells, the most mature component of the MM clone, secrete IL-6 and induce IL-6 production from other cell types. However, the MM clone also includes circulating clonotypic B lymphocytes. Using ELISA and in situ RT-PCR we demonstrate here that, unlike the healthy control B cells, MM B cells express IL-6 mRNA and secrete IL-6 protein. In vitro, MM B cells were the major producers of IL-6 in peripheral blood mononuclear cells. On average, 50% of MM B cells express the IL-6 receptor (IL-6R, CD126), suggestive of autocrine stimulation. They also express CD31, potentially facilitating their paracrine interactions with osteoclast precursors. CONCLUSION: Secretion of IL-6 by circulating clonotypic B cells in MM may contribute to the autocrine and paracrine cytokine networks that maintain the malignant clone and are responsible for disruption of normal bone metabolism in this incurable disease.     

Expression of the bcl-2 family of pro- and anti-apoptotic genes in multiple myeloma and normal plasma cells: regulation during interleukin-6(IL-6)-induced growth and survival

Aberrant expression of genes regulating apoptosis/survival seems to be essential in the stepwise development of human multiple myeloma (MM). In this paper we have compared the expression of bcl-2 family pro- and anti-apoptotic genes in MM cell lines, primary MM cells and normal plasma cells. The Bcl-2, Mcl-1, Bcl-xL/S, Bcl-w, Bax, Bak, and Bad were shown to be expressed in both malignant and non-neoplastic, normal plasma cells. Quantitative analysis revealed that the malignant phenotype seemed to correlate with an elevated expression of Mcl-1, a decreased expression of Bax and, to a lesser extent, an increased Bcl-2/Bax expression ratio. The possible influence of interleukin-6 (IL-6) in regulating the expression of the bcl-2-related genes was also examined. Using the IL-6-dependent MM cell lines U-1958 and U-266-1970 it was clearly shown that IL-6 deprivation induced cell cycle arrest in both cell lines, whereas apoptosis was only detected in the U-1958 cells. Furthermore, the anti-apoptotic proteins Bcl-2, Mcl-1 and Bcl-xL were down-regulated, while the expression of the pro-apoptotic Bax protein was increased. To conclude, we suggest that the expression pattern of the Bcl-2 family of proteins separates the malignant phenotype of MM from normal plasma cells, and that the protecting effect of IL-6 may be conducted via an altered balance between these proteins.     

Targeting NF-kappaB pathway with an IKK2 inhibitor induces inhibition of multiple myeloma cell growth

The pathophysiologic basis for multiple myeloma (MM) has been attributed to the dysregulation of various paracrine or autocrine growth factor loops and to perturbations in several signal transduction pathways including IkappaB kinase/nuclear factor-kappaB (IKK/NF-kappaB). The present study aimed at investigating the effect of a pharmaceutical IKK2 inhibitor, the anilinopyrimidine derivative AS602868, on the in vitro growth of 14 human MM cell lines (HMCL) and primary cells from 13 patients. AS602868 induced a clear dose-dependent inhibition of MM cell growth on both HMCL and primary MM cells, which was the result of a simultaneous induction of apoptosis and inhibition of the cell cycle progression. Combination of AS602868 with suboptimal doses of melphalan or Velcade showed an additive effect in growth inhibition of HMCL. AS602868 also induced apoptosis of primary myeloma cells. Importantly, AS602868 did not alter the survival of other bone marrow mononuclear cells (CD138(-)) co-cultured with primary MM (CD138(+)) cells, except for CD34(+) haematopoietic stem cells. The results demonstrate the important role of NF-kappaB in maintaining the survival of MM cells and suggest that a pharmacological inhibition of the NF-kappaB pathway by the IKK2 inhibitor AS602868 can efficiently kill HMCL and primary myeloma cells and therefore might represent an innovative approach for treating MM patients.     

Differentiation of early plasma cells on bone marrow stromal cells requires interleukin-6 for escaping from apoptosis

The bone marrow (BM) is well known to be the major site of Ig production in secondary immune responses; thus, the microenvironment of BM is considered to be essential for final differentiation of plasma cells. We identified in the peripheral blood (PB) early plasma cells (CD38++CD19+VLA-5-) committed to entering the BM. The sorted early plasma cells rapidly entered apoptosis in vitro, but these cells could survive and further differentiate into mature plasma cells (CD38 CD19+) just as BM plasma cells in the presence of a BM-derived stromal cell line (KM-102). Culture supernatants of KM-102 cell lines could also support survival of these cells, and antibody to interleukin-6 (IL-6) completely blocked the effect of these supernatants. Furthermore, recombinant IL-6, but not IL-1 or IL-3, could support their survival and their differentiation into mature plasma cells (CD38 CD19+VLA-5+) with expression of VLA-5 mRNA. Therefore, here is direct evidence that early plasma cells found in the PB differentiated into mature plasma cells with stromal cell-derived IL-6 in vitro; thus, BM stromal cells control the final checkpoint of plasma cell differentiation with secretion of IL-6 in the BM.     

Paracrine rather than autocrine regulation of myeloma-cell growth and differentiation by interleukin-6

To explore the mechanisms involved in the pathogenesis of human multiple myeloma (MM), we investigated the potential role of interleukin-6 (IL-6), a B-cell differentiation factor in humans, and a growth factor for rat/mouse heterohybridomas and murine plasmacytomas. Using a heterohybridoma assay, we found that two well-documented human myeloma cell lines, RPMI 8226 and U266, did not secrete IL-6 and did not express RNA messengers for IL-6. Neutralizing antibodies to IL-6 did not inhibit their proliferation, and recombinant IL-6 did not stimulate it. Taken together, these data show that IL-6 is not the autocrine growth factor of these human myeloma cell lines. A high production of IL-6 was found in the bone marrows of patients with fulminating MM, compared with patients with inactive or slightly active MM, or to healthy donors. This IL-6 production was assigned to adherent cells of the bone-marrow environment but not to myeloma cells. A spontaneous proliferation of myeloma cells freshly isolated from patients was observed in short-term cultures. Recombinant IL-6 was able to amplify it two- to threefold. The spontaneous proliferation of the myeloma cells was inhibited by anti-IL-6 antibodies and reinduced by recombinant IL-6. After 2 to 3 weeks of culture, the myeloma-cell proliferation progressively declined and no IL-6-dependent myeloma cell lines could be obtained despite repeated additions of fresh IL-6 and costimulation with other cytokines such as tumor necrosis factor (TNF)beta, or IL-1 beta. These data demonstrated a paracrine but not autocrine regulation of the growth and differentiation of myeloma cells by IL-6.     

Role of interleukin-6 in the proliferation of human multiple myeloma cell lines OCI-My 1 to 7 established from patients with advanced stage of the disease

Interleukin-6 (IL-6) has been shown to stimulate the proliferation of multiple myeloma cells purified to a high degree from human bone marrow. IL-6 production in multiple myeloma has been attributed to cells belonging to the myeloma clone, thus supporting a mechanism of autostimulation. In addition, it has been shown that IL-6 may be produced by auxiliary cell populations of the bone marrow that are not part of the myeloma clone. A definitive separation of both putative sources for IL-6 may be difficult to achieve in fresh patient IL-6 growth requirement and production by pure myeloma cell populations using seven human myeloma cell lines (OCI-My 1 to 7) that were established from patients with advanced disease. The proliferative response of each line to recombinant IL-6 was measured in a clonogenic assay providing human plasma and methylcellulose as a viscous support and by 3H-thymidine uptake in liquid suspension culture. We observed marked heterogeneity, ranging from IL-6-dependent colony formation by OCI-My 4, to IL-6-independent growth. All lines expressed mRNA for the IL-6 receptor. Expression of IL-6 mRNA was analyzed after amplification by polymerase chain reaction and was present in five of seven lines. IL-6 protein was detected by enzyme-linked immunosorbent assay (ELISA) in the culture supernatants of two lines (OCI-My 3 and 2). Its functional activity was confirmed in a bioassay using the IL-6-dependent murine hybridoma line B 13.29. This activity was neutralized by anti-IL-6 antibody. Two lines did not express mRNA for IL-6. The remaining three lines expressed mRNA for IL-6, but did not secrete IL-6 protein. Immunoprecipitation experiments with lysates of one of these three lines did not detect the presence of IL-6 protein. These results suggest that autocrine stimulation by IL-6 may occur in some cell lines derived from patients with multiple myeloma. However, it does not represent a universal mechanism in myeloma cell growth.     

Growth mechanism of human myeloma cells by interleukin-6

Human myeloma cells are heterogenous morphologically and phenotypically. Myeloma cells can be classified into at least 5 subpopulations; MPC-1-CD45+CD49e-, MPC-1-CD45-CD49e- immature myeloma cells, MPC-1+CD45-CD49e-, MPC-1+CD45+CD49e- intermediate myeloma cells and MPC-1+CD45+CD49e+ mature myeloma cells. Interleukin-6(IL-6) is a major growth factor for human myeloma cells, but only MPC-1-CD45+CD49e- immature myeloma cells can response directly to IL-6 to proliferate. In the U-266 cell lines, IL-6 can lead to the induction of CD45 expression and CD45+ U-266 cells can proliferate in response to IL-6. In primary myeloma cells, MPC-1-CD45-CD49e- immature myeloma cells sorted from bone marrow samples can be changed to CD45+ cells by addition of IL-6 in vitro. In both CD45- and CD45+ U-266 cells, STAT3 and MAPK(ERK1/2) can be activated in response to IL-6 equally between them, but src family kinases such as Lyn, Fyn can be activated only in CD45+ U-266 cells. Thus, the activation of the src family kinases associated with CD45 expression is a prerequisite for the proliferation of myeloma cells. In the bone marrow of myeloma patients, most myeloma cells do not express CD45, and CD45+ immature myeloma cells are only 1 approximately 2%. In order to clarify the difference of cellular context between CD45- and CD45+ myeloma cells, PCR-based cDNA subtraction was performed from CD45+ U-266 cells to CD45-U-266 cells. The series of this subtraction selected several genes. Furthermore, sensitivity to stress stimuli between CD45+ and CD45- U-266 cells was also compared. CD45-U-266 cells were markedly more resistant to stress conditions such as serum-free condition. Therefore, we can speculate that in the bone marrow of human myelomas IL-6 can induce proliferation of CD45+ immature cells, but the amount of IL-6 is too low to support CD45+ myeloma cells and loss of CD45 results in no direct response to IL-6 to proliferate but confers resistance to stress condition leading to the longer survival at the limited amount of IL-6.     

Acquisition of growth autonomy and tumorigenicity by an interleukin 6-dependent human myeloma cell line transfected with interleukin 6 cDNA.

In human multiple myeloma, an autocrine growth mechanism through interleukin 6 (IL-6) has been advocated. However, growth of myeloma cells in vitro is poor except for established cell lines, and IL-6 autocrine growth is quite rare in myeloma cell lines. In the present study, we devised a model of IL-6 autocrine growth in vitro by transfecting IL-6 cDNA into a human myeloma cell line that had a proliferative response to IL-6 but did not produce IL-6. After IL-6 transfection, the cells proliferated in culture media without IL-6, and their growth rate was elevated at higher cell densities. IL-6 was detected by enzyme-linked immunosorbent assay in the culture media of the transfectants. IL-6 mRNA was distinctly expressed in these cells when analyzed by Northern blotting. The growth of the transfectants was definitely inhibited by anti-IL-6 or anti-IL-6 receptor monoclonal antibodies. Furthermore, the transfectants were successfully transplanted to nude mice. These results indicate that the myeloma cells obtained growth autonomy in vitro through IL-6 and tumorigenicity in vivo, after IL-6 transfection.     

Characterization of an interleukin-6-mediated autocrine growth loop in the human multiple myeloma cell line, U266

It has been reported recently that freshly isolated human myeloma cell cultures proliferate in response to added interleukin-6 (IL-6). Endogenous levels of IL-6 found in the same cultures suggested that an autocrine growth loop may contribute to cell growth. However, the lack of homogenous cell populations in primary myeloma cultures has made it difficult to distinguish between paracrine and autocrine growth mechanisms. To precisely address the autocrine growth issue we have evaluated the growth of the human myeloma cell line, U266. We have found that a neutralizing anti-IL-6 monoclonal antibody can inhibit U266 proliferation. Furthermore, the addition of IL-6 antisense oligonucleotides also inhibits U266 proliferation. These effects are reversed by adding IL-6, suggesting the presence of an autocrine loop. Using bioassays with two different IL-6-dependent cell lines, we were able to detect IL-6 in concentrated U266 supernatants. IL-6 mRNA was detected by polymerase chain reaction amplification of cDNA. Cell cycle parameter analysis shows that IL-6 acts to release a block in G1. Taken together these results present conclusive evidence for IL-6-mediated autocrine growth in the U266 human myeloma cell line.     

Expression and function of Fas (APO-1/CD95) in patient myeloma cells and myeloma cell lines

Cross-linkage of the Fas antigen induces programmed cell death in many normal and malignant lymphoid cells by a process known as apoptosis. In this study, we examined the sensitivity of myeloma cell lines and patient plasma cells to a cytolytic anti-Fas monoclonal antibody (MoAb). Eight of 10 myeloma cell lines were induced to undergo programmed cell death by anti-Fas MoAb as determined by DNA fragmentation and morphologic changes. Of the two myeloma cell lines that were resistant to anti-Fas treatment, one did not express the Fas antigen. Only the U266 cell line expressed Fas, but was not killed by the anti0Fas MoAb. To extend these studies, we have examined the expression and function of Fas in freshly isolated CD38hiCD45neg-int plasma cells from patients with multiple myeloma (MM), monoclonal gammopathy of undetermined significance (MGUS), and primary amyloidosis (AL). By three-color flow cytometry, we found Fas expression in CD38hiCD45neg-int plasma cells from all patient groups to be variable, as Fas was expressed in 15 of 28 MM, 3 of 6 MGUS, and 2 of 7 AL patients. In morphologic studies of apoptosis, Fas-positive myeloma cells in patient bone marrow mononuclear cell (MNC) cultures appeared to be resistant to anti-Fas-mediated apoptosis. By contrast, purified myeloma cells from the same patient were sensitive to anti-Fas treatment, suggesting the presence of a protective factor(s) in unseparated MNC cultures that may inhibit Fas-induced apoptosis of plasma cells. Of interest, serum from normal individuals and myeloma patients also protected myeloma cell lines from undergoing Fas-mediated apoptosis. These studies show that Fas expression in myeloma cell lines and CD38hiCD45neg-int patient plasma cells is variable and may reflect a variance in the maturation status of the various plasma cell populations. Moreover, Fas-mediated killing of patient cells and myeloma cell lines was also variable, which may be influenced, in part, by the presence of a soluble protective factor.     

Targeting receptor kinases by a novel indolinone derivative in multiple myeloma: abrogation of stroma-derived interleukin-6 secretion and induction of apoptosis in cytogenetically defined subgroups

In multiple myeloma (MM), both vascular endothelial (VEGF) and basic fibroblast growth factor (bFGF) promote tumor growth and survival. We have used the novel indolinone BIBF 1000 to study effects of simultaneous inhibition of VEGF, FGF and transforming growth factor-beta on MM cells and their interactions with bone marrow stroma cells (BMSCs). Both, in the absence and presence of myeloma-stroma cell contacts, BIBF 1000 abrogated BMSC-derived secretion of interleukin-6 (IL-6). In addition, BIBF 1000 directly induced apoptosis in t(4;14)-positive cell lines as well as in CD138+ marrow cells from patients with t(4;14) myeloma. To a similar extent, BIBF 1000 induced apoptosis in MM.1S and MM.1R cells carrying the translocation t(14;16). In case of MM.1S and other dexamethasone-sensitive t(14;16) cell lines, BIBF 1000 and dexamethasone had additive proapoptotic effects. Induction of apoptosis by BIBF 1000 was associated with inhibition of the mitogen-activated protein kinases (MAPK) pathway in t(4;14) and inhibition of the phosphatidyl-inositol-3 kinase/AKT pathway in t(14;16) cells. Apoptotic effects did not occur in t(4;14)-or t(14;16)-positive MM cells carrying n- or k-Ras mutations. The data provide the rationale for clinical evaluation of this class of targeted kinase inhibitors in MM with focus on defined cytogenetic subgroups.     

Interleukin-21 is a growth and survival factor for human myeloma cells

Interleukin-21 (IL-21) is a recently cloned cytokine with homology to IL-2, IL-4, and IL-15. In this study we examined the effects of IL-21 on human myeloma cells. We found that IL-21 induced proliferation and inhibited apoptosis of the IL-6-dependent human myeloma cell lines ANBL-6, IH-1, and OH-2. The potency of IL-21 was close to that of IL-6 in the OH-2 cell line. Neutralizing antibodies to IL-6 or the IL-6 receptor transducer chain (gp130) did not affect IL-21-induced DNA synthesis, indicating that IL-21-induced proliferation was not mediated through these proteins. Tumor necrosis factor (TNF), another stimulator of myeloma cell growth, up-regulated the expression level of IL-21 receptor (IL-21R), and combinations of TNF and IL-21 gave synergistic effects on myeloma cell proliferation. Furthermore, 4 of 9 purified samples of primary myeloma cells showed a significant increase in DNA synthesis on stimulation of the cells by IL-21. By Western blot analysis, we demonstrated that the intracellular signaling pathways of IL-21 in myeloma cells involved phosphorylation of Jak1, Stat3, and Erk1/2 (p44/42 mitogen-activated protein kinase). IL-21 is a novel growth and survival factor in multiple myeloma and may represent a target for future therapy.